The term Guided Motion Knees was formulated in the mid-1990's in an effort to conceptualize features in the femoral and tibial components of a total knee replacement (TKR) which would guide the motion of the knee during flexion and extension. The particular motion characteristics of interest were those on a natural anatomic knee itself; as the knee is flexed, posterior displacement (or rollback) of the femur on the tibia, external rotation of the femur on the tibia, and rotational and anterior-posterior laxity at all angles of flexion. Guided Motion in a basic form has already been addressed in many previous designs dating back to the early 1970's, using the geometry of the lateral and medial bearing surfaces, as well as central cam-post mechanisms. (Raymond P. Robinson, The Early Innovators of Today's Resurfacing Condylar Knees, Journal of Arthroplasty, Vol. 20, Suppl 1, 2005). Almost all of the total knee replacements on the market today have similar shapes for the lateral and medial sides, such that there is little lateral or medial bias to the motion. However, in recent years, designs have emerged which have attempted to produce asymmetric motion. One of the first was the Medial Pivot Knee (based on early concepts by Freeman et al., Wright Manufacturing) and the Journey Knee (Smith & Nephew). The Medial Pivot Knee is based on a completely stable medial side and a rotatable lateral side. The Journey Knee has more conformity medially than laterally with a slightly convex lateral tibial surface, together with a cam-post mechanism to produce femoral rollback with flexion. There is evidence that these designs do bring knee kinematics and function closer to natural anatomic than symmetric designs. However, there continues to be a need for a total knee replacement which, more perfectly, reproduces normal kinematics and function, and feels like a natural knee.